搜题请搜索小程序“爱下问搜题”
问题 选择题

（4分）（2012•茂名）醋酸（CH3COOH）是一种重要化工原料．下列有关醋酸的说法中正确的是（　　）

A．醋酸属于无机化合物

B．醋酸中碳，氢元素的质量比为6：1

C．醋酸中氧元素的质量分数约为68.2%

D．每个醋酸分子是由8个原子构成

答案

BD

A、由醋酸（CH3COOH）的化学式可知，醋酸是含碳元素的化合物，属于有机化合物，故选项说法错误．

B、醋酸中碳、氢元素的质量比为（12×2）：（1×4）=6：1，故选项说法正确．

C、醋酸的相对分子质量为12×2+1×4+16×2=60，醋酸中氧元素的质量分数约为100%=53.3%，故选项说法错误．

D、由醋酸化学式可知，每个醋酸分子是由2个碳原子、4个氢原子、2个氧原子构成的，每个醋酸分子是由8个原子构成，故选项说法正确．

故选BD．

单项选择题

对于DNA的半不连续合成，不正确说法是

A．随从链的合成迟于前导链的合成

B．随从链是不连续合成的

C．不连续合成的片段为冈崎片段

D．前导链和随从链合成中均有一半是不连续合成的
查看答案
单项选择题

During the past years, intelligent technology has evolved (116) three generations. The first was characterized by tools such as prolog and OPS. prolog is a simple backward-chaining environment, and OPS is a simple forward-chaining environment. This led to the second generation of knowledge-engineering environments. Its goal was to model, prototype and construct (117) systems.

All three generations were oriented toward generic (118) and represented generalized implementation environments for the construction of expert systems. knowledge bases and AI applications.Some of the solution-oriented products are also seamlessly integrated with generic knowledge-engineering environments, permitting end users to add (119) rules and objects, as well as predefined knowledge-based logic to address problems in manufacturing simulation.Marketplace orientation is rapidly (120) toward solution-oriented intelligent product environments. the fourth generation represents a new line of thinking and ’ develop-merit by commercial fu-ms. will reduce the cost risk and development time associated with problem solving.

（117）是（）

A. custom

B. knowledge

C. through

D. problem solving
查看答案